Cathode-ray projector tube



1, 1948. c. s. SZEGHO 2,448,476

CATHODE-RAY PROJECTOR TUBE Filed Dec. 3, 1943 4 I N V EN TOR.omsa/zaizhwi Jzeyko Patented Aug. 31, 1948 2,448,476 l CATHODE-RAYPROJECTOR TUBE Constantin S. Szegho, Chicago, Ill., assignor to .TheRauland Corporation,

poration of Illino Chicago, 111., a cor- Application December 3, 1943,Serial No. 512,710

1 i This invention relates to new and useful improvements in cathode rayprojector tubes. 7

An object of the invention is a cathode ray tube having a fluorescentscreen'consisting oftwo or more layers of fluorescent material andadapted to project a clear, large image on the customary viewing screen.

A second object of the invention is to devise a glow. The cathode raybeam excites the blue layer which then emits light to excite the yellowlayer.

In end view cathode ray tubes, first the yellow layer is applied to theglass bulb and then on top of it the blue layer. It is the yellow layerthat has the desired long after-glow, when exited by light given off bythe blue layer. The glass window and the low secondary emission factorof the fluorescent screen deposited thereon cause the screen to acquirea negative charge when bombarded with high voltage electrons which arealways present in projection tubes. The use of this arrangement forprojection on a large viewing screen is, therefore, not practicable.

It has been suggested to place the yellow fluorescent layer on theviewing screen outside of the bulb enclosing the cathode ray tube andapply only the blue layer to the end wall of the bulb. However, inaddition to the disadvantages mentioned, the fluorescent material on thescreen cannot be enclosed within a moisture proof container.

In accordance with the present invention, the problem is solved byproviding two or more layers of fluorescent material within a cathoderay tube which is provided with the elements of a Schmidt camera soarranged that the image of a long after-glow layer can be projected onthe viewing screen.

In order more fully to explain the nature of the invention, anembodiment thereof will now be described as applied to the drawing whichdiagrammatically illustrates a tube in vertical cross-section.

camera. Between these two elements is located.

within the envelope a convex conductive support l4 carrying thecustomary blue layer l'3 andyelilow layer I3a, but in a reversed order,theyellhW layer being nearest to the gun. These laylemofr fluorescentmaterial are in alignment witlnascenstral opening l5 in the mirror I Iand they, as will as their mounting plate M, are supported, by arms; Mafrom the side walls of the cylinder Ii]. The shapes of the mirror II andof the plate l2 and their position with respect to one-another and withrespect to the fluorescent layers, should be determined in accordancewith the practice wellknown in the construction of Schmidt camera typeof optical systems. A neck H5 is attached to the mirror II andcommunicates with the envelope l0 through the central opening l5.Theneck encloses the usual electron gun I! and has. associated with itthe customary vertical and hurl--- zontal deflecting means [8 and H3.

The cylinder I0 may be of glass, metal, or ce'- ramic material, and theenvelope may be either evacuated and sealed off or .it may becontinuously pumped.

The image appearing on layer l3a will be reflected by the mirror Itthrough the correcting plate l2 without interference from any refractingor absorbing medium and can thus be projected on the customary viewingscreen through a suitable optical system.

The voltage applied to the electron gun should be such that theelectrons penetrate the yellow layer l3a and lose the major part oftheir energy in the blue layer l3. By controlling the voltage applied tothe accelerating anode Ila of the electron gun ll, the velocity of theelectrons can be controlled. Thus the depth of penetration and theduration of the after-glow is also controlled.

A cathode ray tube of the type herein illustrated, is shown in myco-pending application, Serial N 0. 442,835. Many other types of cathoderay tubes of this general nature are illustrated in said application andmay be adopted to good advantage for the purposes of the presentinvention.

What is claimed is:

1. In combination, two superimposed convex fluorescent layers the firstlayer having a long afterglow as related to the afterglow of the secondlayer, a support therefor, an electron gun emitting electrons whichtraverse the first layer and excite the 's'econdilayer, an evacuatedencent surfaces, a support therefor, an electron for generatingelectrons traversing the first and exciting the second surface, amirror;or -refiecti-1-,., ing light emanating from the first surface, a.correcting plate in the path of the lig ht' raysrefiected by saidmirror, an evacuated envelope enclosing said surfaces and having a wallmade up of the mirror, an opposite wall madeu-pofasaidvcor recting plateand a neck enclosing saidgun and, projecting through a central aperturein said" correcting plate.

4. The device defined in claim 3, and'in which thefirst one of saidsurfaces hasanafter-glow whichis long, relative tothat of the second,

5. Incombination, anelectron gunemittinga streamof electrons, a firstlayer-of fluorescentmaterial through which said streamof electronspasses without substantial 10ss-of electrons, a second layer offluorescent. material excited by said-stream of electrons stopping: init, the sec-- ond-layer contacting the first layer and the light fromthe second layerexciting the first, a support for said layers, anevacuated-envelope enclosingsaid. layers, support and gun,andmeansincluding a mirror and correcting plate for projecting the imageappearing on the first layer.

6. A device according to claim 5 and in which the first layer comprisesa blue fiuorescing ma.- terial and the second layer a yellow fiuorescingmaterial, the afterglow of the first layer being long as compared to theafterglow of the second layer.v

CONSTANTIN S. SZEGHO.

REFERENCES CITED The;followingvreferences are of record in the filacfthis pat nt:

UNITED STATES PATENTS Number Name Date 2,096,986 if Von Ardenne Oct. 26,1937 2,099,023,, Levy Nov. 16, 1937 2,137,118 Schleede etal. Nov. 15,1938 2,177,691 Dawihl et al Oct. 31, 1939 2,243,828" Leverenz May'27,"1941 2, 295,7-79'-- Epstein-et a1.- Sept.- 15,1942? 2,305,855 Epstein-et al. Dec. 22,' 1942 2,307,183 Bedford .4 Jan; 5; 1943- 2,330,172Rosenthal- Sep-t. 21, 1943 2,372,359 Cook' Mar.-27',"19,45$

FOREIGN PATENTS.

Number Country Date-:1,

443,788 Great=Britain.' Mar.15,-1936:* 463,891 Great Britain.- Apr.8;.1'937: 4:37,;241' Great: Britain; ,,June.16;;1938 640;05.6 Germany';-o Dec; 21;.1 936.:

